1. Field of the Invention
The present invention relates to a method of producing an instantly soluble powder; more specifically, it relates to a method of producing an instantly soluble powder according to vacuum freeze-drying.
Further, the present invention relates to a method of producing an instantly soluble powder (an instant tea powder) having an excellent solubility, flavor and taste.
Incidentally, "tea" according to the present invention is defined to include tea, such as green tea, black tea, oolong tea, toasted tea, and brown rice tea.
2. Description of the Prior Art
Conventionally, tea powder, coffee powder and the like have been produced by putting materials such as tea leaves and coffee beans into an extraction tank to extract with hot water, and, after the separation of an extract solution, condensing the extract in the extract solution to a proper concentration, or adjusting the concentration with dextrin or the like, and then drying the resultant product according to spray drying or vacuum freeze-drying. However, they have some problems in flavor when they are drunk in hot water; namely, those with dextrin added therein are given flavors different from the original flavors of tea and coffee, and those dried according to spray drying are poor in flavor which is the special feature of tea and coffee, and particularly a light flavor disappears.
Hence, a method has been devised for the purpose of solving the problems in flavor, which comprises condensing the extract without dextrin, or using the extract solution thickly extracted as it is, and subjecting it to vacuum freeze-drying to produce a powder. However, when hot water is poured onto a tea powder and a coffee powder obtained by freezing a solution as it is and subjecting it to vacuum freeze-drying, they tend to give rise to coagulations, and it is necessary to stir them up to dissolve them in hot water completely. In addition, when water is poured there upon, they hardly dissolve by mixing them up.
One example of prior arts is a method of producing an instant tea (Official Gazette of Japanese Laid-Open Patent Publication No 64-86832/1989) comprising condensing the extract extracted from tea leaves to adjust the concentration to 15 to 60 weight % and freeze-drying it, but the said method comprises giving rise to a specific amount of crystals of ice in a condensate and then freeze-drying it, and solubility is not improved even though it becomes a powder with less foam formation.
The present inventors have developed some techniques for the purpose of solving these problems. For example, the following can be exemplified: an instantly soluble powder (Official Gazette of Japanese Laid-Open Patent Publication No.63-3755/1988) having an excellent flavor and taste, which comprises extract obtained from tea leaves by water extraction, extract obtained from tea leaves by distillation or extraction with a solvent and a powder of tea leaves, a method of producing an instantly soluble powder (Official Gazette of Japanese Laid-Open Patent Publication No.63-94960/1988) having an improved solubility, which comprises subjecting an aqueous solution containing a solids constituent to vacuum freeze-drying incompletely, subjecting it to a dissolving treatment and then subjecting it to vacuum freeze-drying again, and a method of producing a powder being of high quality and instantly soluble (Official Gazette of Japanese Laid-Open Patent Publication No.63-167742/1988), which comprises subjecting a flavorous beverage with less than 5 weight % of the solids content to vacuum freeze-drying, pressing the said dried product, pulverizing it into a powder and, if required, sifting it. The present inventors have continued to make studies upon these techniques and have finally developed a method of producing an instantly soluble powder having an excellent solubility, flavor and taste.